The invention relates to a contact-making system for two printed circuit boards which, for reciprocal contact-making, each have a contact region with contact elements.
A printed circuit board has a number of conductor tracks via which a functional element or an assembly is supplied and/or driven. In order to wire up and interconnect the individual functional elements or assemblies, for example in an on board electrical system of a motor vehicle, connecting elements or contact-making systems are provided via which printed circuit boards are connected to one another or a printed circuit board is connected to a conventional connector. The printed circuit boards have a rigid supporting layer, for example, on which the conductor tracks are applied or they are designed as flexible printed circuit boards for example in the form of conductor sheets with applied, in particular etched, conductor tracks.
Reliable and permanent contact-making is always necessary in order to maintain the functional reliability. This is particularly applicable in the automotive sector, where severe temperature fluctuations and vibrations occur. What is crucial for reliable contact-making is that the individual contact regions and contact elements of the elements that are to be connected to one another are positioned with great accuracy with respect to one another in the joining-together process. A high positioning accuracy has the advantage that the contact areas overlap one another to a great extent, a low contact resistance thereby being attained. On the other hand, the positioning accuracy has the effect that the spacing from neighboring contact elements is kept large enough to keep the risk of short circuits low.
The task of positioning a printed circuit board relative to a further printed circuit board or else to the contact areas of a connector is generally undertaken by a contact-making or connector housing. European Patent Application EP A 0 849 120, European Patent Application EP A 0 717 462, corresponding to U.S. Pat. No. 5,632,646 to Ii et al., German Published, Non-Prosecuted Patent Application DE A 199 05 064, corresponding to U.S. Pat. No. 6,017,244 to Daane, and German Utility Model DE U 298 23 576 disclose special contact-making housings for positioning printed circuit boards.
EP A 0 849 120 provides for the printed circuit board to be pushed into a slotted housing in such a way that a cutout of the printed circuit board in a contact region is aligned with a channel guided through the housing. Contact is made with the conductor track via a contact pin which is guided through the channel and the printed circuit board. The contact pin has a larger diameter than the cutout, thereby ensuring that contact is made. Therefore, the positioning is effected by way of the interaction of the contact pin guided in the channel with the cutout.
EP A 0 717 462 provides for the printed circuit board to be pushed into a conically tapering receptacle region of a contact-making housing, so that the printed circuit board is slightly curved and cannot be shifted within the contact-making housing. The printed circuit board is thus guided by the contact-making housing in this case.
DE A 199 05 064 and DE U 298 23 576 are concerned with the mutual contact-making of two printed circuit boards. Here, too, the task of positioning is undertaken by a contact-making housing. In accordance with DE A 199 05 064, the printed circuit boards are clamped in between two clamping jaws, centering pins being integrally formed on one of the clamping jaws, which pins are guided through cutouts in the printed circuit boards and engage in corresponding centering holes on the opposite clamping jaw. The clamping jaws have a structured surface which is impressed on the printed circuit boards in the form of an undulatory profile. DE U 298 23 576 discloses inserting one printed circuit board into a cutout in an upper housing half and positioning the second printed circuit board with respect to a lower housing half via centering pins of the latter, the centering pins of the lower housing half engaging in centering holes in the upper housing half. In order to ensure a sufficient contact pressure for a good contact, the lower housing half has spring means which act on the contact elements of the printed circuit boards. Contact bulges are provided for this purpose, the spring means engaging in said contact bulges, so that the contact bulges are pressed against the individual contact elements of the second printed circuit board.
What all the known embodiments have in common is the fact that the positioning is effected via the contact housing. Therefore, the positioning accuracy depends inter alia on the dimensional accuracy of the housing and, in particular, on the tolerances of the conductor tracks relative to the mechanical positioning elements. Reducing the tolerances for the purpose of increasing the positioning accuracy can only be achieved by complicated means, such as, for example, mechanical design changes to the contact-making housing.
An alternative option for positioning is optical position control, in which an automatic component-mounting machine determines the position optically. However, both technically and economically this method is practical only for undetachable permanent standard connections.
The invention is based on the object of specifying a contact-making system for two printed circuit boards with which a high positioning accuracy can be achieved.
The object is achieved according to the invention by means of a contact-making system for two printed circuit boards which, for reciprocal contact-making, each have a contact region with contact elements, in which case, for the positioning of the printed circuit boards, the two contact regions are three-dimensionally structured complementarily with respect to one another.
The essential underlying idea is to be seen in the fact that the function of positioning is taken care of by the contact regions themselves, so that positioning relative to housing parts is obviated. This necessarily obviates the problems which stem from tolerances between the conductor track pattern and the positioning elements. Thus, instead of positioning relative to a housing, the conductor track pattern itself is used as positioning element. The special three-dimensional structuring is provided for this purpose, through which, on account of the complementary configuration in particular of contact elements that are to be contact-connected to one another, automatic positioning is effected in the joining-together process. The two contact regions thus have elevations and depressions which define their position with respect to one another. The complementary three-dimensional structure permits a simple, reliable and fast joining-together process with high positioning accuracy of the two printed circuit boards.
In a preferred embodiment, the contact elements on the printed circuit boards form an elevation, so that the printed circuit boards are spaced apart from one another in the joined-together state. In this case, the height is chosen in such a way that, under a specific contact pressure, all the contact areas of the contact elements touch one another and further elements on the printed circuit board such as e.g. solder resist or uncovered conductor tracks do not touch one another, high functional reliability thereby being achieved.
In this case, the contact elements are preferably embodied as planar structural parts made of conductive material and are either applied in the form of laminae to the conductor tracks, for example by a soldering operation, or else formed by an embossing operation. If only low currents are to be transmitted, then carbon-filled plastic is also suitable, in particular, as a material for the contact elements. By way of example, the contact elements are embodied solidly in the form of a cube, a parallelepiped or a disk. Their contact area is preferably roughened in order to reduce the contact resistance. As an alternative to a contact area of planar design, complementary contact elements have a bulge and a complementary indentation in the region of their contact areas. This shaping results in self-centering of the contact element pair.
The contact elements, for forming the three-dimensional structure, preferably have different heights, the total height of the contact element pairs formed by complementary contact elements being identical. The different heights serve for positioning and the constant total height ensures that reliable contact is made with all the contact elements.
For the highest possible positioning accuracy, it is advantageous to provide at least two complementary contact element pairs which have a large spacing from one another; in particular, they are arranged on opposite end regions of the printed circuit boards.
In order to achieve reliable and permanent contact-making, a preferred embodiment provides for at least one contact element of a contact element pair to be of elastic design. In particular, the contact element is configured resiliently or as a spring. For this purpose, the contact element is, for example, constructed in two parts, the first part undertaking the actual contact-making and the other part ensuring the elasticity. Within a certain tolerance range, height differences between the two printed circuit boards can be bridged without difficulty by virtue of the elastic or resilient design.
For the same purpose, simultaneously or alternatively at least one of the printed circuit boards is of elastic design, so that the height tolerance compensation is automatically performed additionally or alternatively by one or by both printed circuit boards in the joining-together process. The printed circuit board of elastic design is thus pliant or flexible.
In accordance with a further preferred embodiment, in addition to the function purely of contact-making, a further function is also integrated in the contact region. For this purpose, at least one of the contact elements comprises an electronic component, which may be either an active or a passive component. By way of example, this component realizes the function of current limiting, of a series resistor, of rectification or of overtemperature protection. If a piezoactive element is used as the component, then a pressure-sensitive contact element, for example, is realized.
In a particularly advantageous refinement, a mask for arrangement between the printed circuit boards is provided, which has passage openings for the contact elements. Such a mask is composed of non-conducting material such as plastic or ceramic. As a result, on the one hand reliable insulation of neighboring contact elements is realized and, on the other hand, the relative movement of the printed circuit boards with respect to one another is limited within the production tolerances. Since the printed circuit boards are preferably pressed together by means of a contact-making housing, all degrees of freedom of movement of the printed circuit boards with respect to one another are limited and, consequently, reliable and permanent contact-making is achieved.
In preferred alternative embodiments, the mask is embodied either as an autonomous element in the form of a stencil for insertion between the two printed circuit boards or as a constituent part of at least one of the two printed circuit boards. In the first case, the stencil is particularly simple and light to produce and, in particular, it is part of a contact-making housing which is preferably a plastic injection-molded part. In conjunction with the stencil, the contact-making housing at the same time performs a protection function for the contact region, provides for strain relief and brings about a sufficiently high contact pressure.
If the mask is embodied as a constituent part of one of the printed circuit boards, then the number of structural parts is reduced. For this purpose, a resist, for example, is applied to the printed circuit board and is removed in the region of the contact-making elements using suitable methods.
Preferably, with the printed circuit boards joined together, the thickness of the mask maximally reaches the total height of the contact element pairs, thereby ensuring that contact is made with the individual contact elements. For this purpose, the mask has, for example, a thickness which is slightly less than the total height, thereby ensuring reliable guidance of the contact elements through the mask.
The masks is preferably made of an elastic material and has, in particular, a thickness which exceeds the total height of the contact element pairs. When the printed circuit boards are joined together, the elastic mask is then compressed and preferably performs a sealing function, so that the contact region is sealed toward the outside.
In order to produce reliable contact-making, a contact pressure is preferably exerted on the printed circuit boards by a contact-making housing in the joined-together state. In particular, the contact-making housing has an elastic region in the contact-making region, so that height tolerance compensation can be effected in the event of production-dictated height differences between the individual contact elements. The contact-making housing thus acts with a spring force on the contact-making region.
The concept of the intrinsic positioning of the contact regions with respect to one another by means of complementarily designed, three-dimensional structures is preferably also provided for printed circuit boards with which contact can be made on both sides and which are arranged in a layered manner one above the other. In particular, three to five printed circuit boards of this type are arranged in a layered manner.
Exemplary embodiments of the invention are explained in more detail below with reference to the drawings.